1. Field of the Invention
The present invention relates generally to optical fiber devices and methods, and in particular to improved systems and methods for creating localized refractive index modulations in an optical fiber.
2. Description of Prior Art
Certain optical devices, such as long-period gratings (LPGs), are fabricated by creating a series of modulations in the refractive index profile of a segment of an optical waveguide. LPGs have been made using a number of different techniques, including the following: exposure to ultraviolet (UV) light, CO2 laser heating; femtosecond laser heating; and electrical arcing in a fusion splicer. FIG. 1 shows a diagram of a system 20 in which a CO2 laser 22 is used to “write” a grating structure into an optical fiber 24. The fiber is loaded into a translator assembly 26 that moves the fiber 24 in the CO2 laser beam 28 with some modulation.
Currently used techniques typically require costly equipment, in addition to the fiber translator assemblies. These techniques also suffer from a number of other drawbacks. For example, the use of UV light techniques may result in hydrogen loading. CO2 lasers and fusion splicers typically deliver non-uniform heat to a fiber, resulting in a modulation that is not rotationally symmetric, thereby potentially introducing an undesirable polarization dependence into the fabricated device. Also, there are safety issues when using lasers.